This idea seems similar to the Committee-driven MEV Smoothing proposal, is that similar to your thinking?
To my mind, there is a non-neglible risk of a single dominant block builder. Who that block builder is may change over time, but the role will remain largely the same. Hopefully the worst negative externalities of a monopolistic block builder will not come to pass, but if they do, they could include censorship-as-a-service techniques such as:
- Favoring one L2 over another (e.g.: block builder: “I’ll push all transactions with significant calldata into every third block, except your transactions - for a fee”)
- prioritizing withdrawals from certain exchanges over other ones (for a fee)
- delaying all transactions to one or two specific high-volume liquidity pools, and putting them all in one block to benefit fro a larger price impact
- demanding higher fees for time sensitive transactions
- etc.
I’ll admit I haven’t thought through these scenarios on a deep level so it would be great to get some other perspectives. That being said, MEV smoothing techniques and other fair-ordering techniques may not fully solve these issues (if they do become issues of course - for now it’s purely theoretical).